Let me start by welcoming you to SBW!! This is a great site with enough combined knowledge to answer just about ANY bike related (and most non-bike related) questions you may have.
It's good to see another Aussie on board, especially a QLD'er!!! I'm about an hour south of Brisbane.
Now, about your intended bike. I originally was heading for a cruiser style bike, like the Kawasaki Eliminator, which is a 250cc. However, after sitting on one, I found I HATED the seating position of cruisers and went looking at sport bikes instead. My fiance, who started riding the same time as myself, couldn't stand the position either.
After sitting on just about every model available, new and old, we settled on the ZZR 250. It has a more upright position that the CBR, etc, which just felt "right" for us. Being that you're coming from a dirt bike, it might be a feel you'd enjoy. Ours is a '99 model (red and black), bought for $5000, but it only had 11,000 km's on it.
As for power, it's only got 40hp. I weigh 85kg (187lbs), but it didn't stop me from winding that little thing out to 160km/h (100mph). It pulls quite hard for a little bike and I've embarrassed quite a few young guys who thought their jap import cage was quick. It's also left the odd HD rider with egg on his face. Mrs Tree and I often went two-up on it also. She's 50kg (110lbs), so we had about 135kg (300lbs) on it. It still went up Tamborine with ease and also took us up to Maleny. It was my daily rider to work (130km return), but I've done up to about 300km on it in one day.
It's got an 18L tank (16L main + 2L reserve) and gets around 320km on the main (depending how you ride
Anyway, I've rambled on long enough. My only other suggestions are these:
1. Go do a Q-Ride course. We did ours at Pro Honda, under Grant. He was fantastic.
2. Don't forget to budget for gear.
Take it easy.